Priority is claimed on Japanese Patent Application No. 2004-70789 filed on Mar. 12, 2004, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical element, a compound optical element, and an illuminating apparatus which forms diffuse illuminating light radiated from a light source into substantially parallel light.
2. Description of Related Art
A large number of light-condensing illuminating apparatuses such as image projection apparatuses and strobe lights employing reflective mirrors and lenses and the like have been proposed for efficient condensing of diffuse light from LEDs (Light Emitting Diodes), mercury lamps, filaments and the like.
Illuminating apparatuses employing primary and auxiliary reflecting mirrors for improved efficiency in condensing reflected light have been proposed (see, for example, Japanese Examined Patent Application, Second Publication No. H04-18406, and Japanese Unexamined Patent Application, First Publication No. 2001-125197). In these illuminating apparatuses, a plurality of reflecting mirrors are positioned in the same orientation in relation to the light source, and light at angles not previously employed is effectively employed.
Furthermore, illuminating apparatuses in which condensing efficiency is improved with lenses and prisms have also been proposed (see for example, Japanese Unexamined Patent Application, First Publication No. 2002-333656, and Japanese Unexamined Patent Application, First Publication No. H04-138438). These illuminating apparatuses form light in which the angle of light from the light source is almost perpendicular to the radiating surface, into a parallel light with a lens, and reflect light having a wider angle using total reflection of a prism, to radiate it from the radiating surface.
Moreover, illuminating apparatuses in which the condensing efficiency is improved with prisms only, have also been proposed (see for example, Japanese Unexamined Patent Application, First Publication No. H10-115853, and Japanese Unexamined Patent Application, First Publication No. H11-146142). These illuminating apparatuses guide light by total reflection within the prisms, and radiate light from the radiating surface.